Utilization of Electrical Energy

A 220 V, 20 kW dc shut motor running at its rated speed of 1200 rpm is to be braked by reverse current braking. The armature resistance is 0.1 Ω and the rated efficiency of the motor is 88%. Calculate: (i) The resistance to be connected in series with the armature to limit the initial braking current to twice the rated current. (ii) The initial braking torque. (iii) The torque when motor falls to 400 rpm.